Electric water pump

ABSTRACT

An electric water pump apparatus may include a body having a stator chamber and a rotor chamber therein, a stator having a hollow cylindrical shape and being disposed in the stator chamber and generating a magnetic field, wherein the stator fluidly insulates the stator chamber and the rotor chamber, a rotor disposed in the rotor chamber and enclosed by the stator, wherein the rotor is rotated by the magnetic field, and a pump cover connected to the body and forming a volute chamber therein, wherein the volute chamber and the rotor chamber are fluidly-communicated through a connecting hole formed to the body and a coolant is supplied to the rotor chamber through the connection hole, wherein the stator includes a stator groove formed in an inner circumference therein and the stator groove is fluid-connected to the rotor chamber and the volute chamber through the connection hole.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2009-0112236 filed on Nov. 19, 2009, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric water pump. Moreparticularly, the present invention relates to an electric water pumphaving improved performance and durability.

2. Description of Related Art

Generally, a water pump circulates coolant to an engine and a heater inorder to cool the engine and heat a cabin. The coolant flowing out fromthe water pump circulates through and exchanges heat with the engine,the heater, or the radiator, and flows back in the water pump. Such awater pump is largely divided into a mechanical water pump and anelectric water pump.

The mechanical water pump is connected to a pulley fixed to a crankshaftof the engine and is driven according to rotation of the crankshaft(i.e., rotation of the engine). Therefore, the coolant amount flowingout from the mechanical water pump is determined according to rotationspeed of the engine. However, the coolant amount required in the heaterand the radiator is a specific value regardless of the rotation speed ofthe engine. Therefore, the heater and the radiator do not operatenormally in a region where the engine speed is slow, and in order tooperate the heater and the radiator normally, the engine speed must beincreased. However, if the engine speed is increased, fuel consumptionof a vehicle also increases.

On the contrary, the electric water pump is driven by a motor controlledby a control apparatus. Therefore, the electric water pump candetermines the coolant amount regardless of the rotation speed of theengine. Since components used in the electric water pump, however, areelectrically operated, it is important for electrically operatedcomponents to have sufficient waterproof performance. If the componentshave sufficient waterproof performance, performance and durability ofthe electric water pump may also improve.

Currently, the number of vehicles having an electric water pump istending to increase. Accordingly, various technologies for improvingperformance and durability of the electric water pump are beingdeveloped.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY OF THE INVENTION

Various aspects of the present invention are directed to provide anelectric water pump having advantages of improved performance anddurability and to provide an electric water pump which minimizesmagnetic flux leakage of a permanent magnet by optimizing a shape of arotor core.

In an aspect of the present invention, the electric water pump apparatusmay include a body having a hollow cylindrical shape and including astator chamber and a rotor chamber therein, a stator having a hollowcylindrical shape and being disposed in the stator chamber andgenerating a magnetic field according to a control signal, wherein thestator fluidly insulates the stator chamber and the rotor chamber, arotor disposed in the rotor chamber and enclosed by the stator, whereinthe rotor is rotated by the magnetic field generated at the stator, anda pump cover connected to the body and forming a volute chamber therein,wherein the volute chamber and the rotor chamber arefluidly-communicated through a connecting hole formed to the body and acoolant having flowed into the volute chamber is supplied to the rotorchamber through the connection hole, wherein the stator includes astator groove formed in an inner circumference therein and the statorgroove is fluid-connected to the rotor chamber and the volute chamberthrough the connection hole.

The rotor core having a hollow cylindrical shape may include a couplinggroove formed along an inner circumference in a length direction thereinand the rotor core is splined to the shaft through the coupling groove.

The stator may include a stator core having a hollow cylindrical shapeto receive the rotor therein and provided with the stator groove at aninner circumference thereof along a length direction, and a stator casemounted at both distal ends of the stator core, wherein the stator caseis made of a bulk mold compound including a potassium family that has alow coefficient of contraction.

The stator case may be provided with a fixing groove and a driverproviding the control signal is slidably and detachably coupled thereto.

The rotor may include a rotor core having a hollow cylindrical shape toreceive a shaft therein, and provided with a plurality of recessesformed by a plurality of guiding protrusions formed at an exteriorcircumference thereof along a length direction, a plurality of permanentmagnets respectively mounted in the plurality of recesses of the rotorcore, a rotor cover mounted at both distal ends of the rotor core andthe plurality of permanent magnets so as to fix the rotor core and theplurality of permanent magnets each other, and a rotor case enclosing anexterior circumference of the rotor core and the plurality of permanentmagnets so as to fix the rotor core and the plurality of permanentmagnet each other in a state that the rotor core and the plurality ofpermanent magnets are mounted at the rotor cover, wherein the rotor casemay be made of a bulk mold compound including a potassium family thathas a low coefficient of contraction.

The plurality of permanent magnets may be mounted in such a manner thatN pole and S pole are alternatively disposed.

The rotor cover may be provided with a plurality of balance holes androtational balance of the rotor may be kept by changing positions of thebalance holes.

In addition, the stator case may be provided with a plurality of balanceholes and rotational balance of the stator may be kept by changingpositions of the balance holes.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description of the Invention, which togetherserve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary electric water pumpaccording to the present invention.

FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1.

FIG. 3 is a perspective view showing a stator of an exemplary electricwater pump according to the present invention.

FIG. 4 is a perspective view of a rotor cover used in an exemplaryelectric water pump according to the present invention.

FIG. 5 is a perspective view showing a shape of a rotor core used in anexemplary electric water pump according to the present invention.

FIG. 6 is a schematic diagram showing processes for mounting rotorcovers to both ends of a rotor core and a permanent magnet in anexemplary electric water pump according to the present invention.

FIG. 7 is a schematic diagram showing processes for manufacturing arotor used in an exemplary electric water pump according to the presentinvention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

An exemplary embodiment of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of an electric water pump according to anexemplary embodiment of the present invention, and FIG. 2 is across-sectional view taken along the line A-A in FIG. 1.

As shown in FIG. 1 and FIG. 2, an electric water pump 1 according to anexemplary embodiment of the present invention includes a pump cover 10,a body 30, a driver case 50, and a driver cover 70. The body 30 isengaged to a rear end of the pump cover 10 so as to form a volutechamber 16, the driver case 50 is engaged to a rear end of the body 30so as to form a rotor chamber 38 and a stator chamber 42, and the drivercover 70 is engaged to a rear end of the driver case 50 so as to form adriver chamber 64.

In addition, an impeller 22 is mounted in the volute chamber 16, a rotor200 (referring to FIG. 7) fixed to a shaft 82 is mounted in the rotorchamber 38, a stator 101 is mounted in the stator chamber 42, and adriver 80 is mounted in the driver chamber 64. The shaft 82 has acentral axis x, and the rotor 200 as well as the shaft 82 rotate aboutthe central axis x. The stator 101 is disposed coaxially with thecentral axis x of the shaft 82.

The pump cover 10 is provided with an inlet 12 at a front end portionthereof and an outlet 14 at a side portion thereof. Therefore, thecoolant flows in the electric water pump 1 through the inlet 12, and thepressurized coolant in the electric water pump 1 flows out through theoutlet 14. A slanted surface 18 is formed at a rear end portion of theinlet 12 of the pump cover 10, and a rear end portion 20 of the pumpcover 10 is extended rearward from the slanted surface 18. The rear endportion 20 of the pump cover 10 is engaged to a cover mounting portion44 of the body 30 by fixing means such as a bolt B. The slanted surface18 is slanted with reference to the central axis x of the shaft 82, andan intersecting point P of lines extended from the slanted surface 18 islocated on the central axis x of the shaft 82.

The volute chamber 16 for pressurizing the coolant is formed in the pumpcover 10, and the impeller 22 for pressurizing and discharging thecoolant through the outlet 14 is mounted in the volute chamber 16. Theimpeller 22 is fixed to a front end portion of the shaft 82 and rotatestogether with the shaft 82. For this purpose, a bolt hole 29 is formedat a middle portion of the impeller 22 and a thread is formed at aninterior circumference of the bolt hole 29. Therefore, an impeller bolt28 inserted in the bolt hole 29 is threaded to the front end portion ofthe shaft 82 such that the impeller 22 is fixed to the shaft 82. Awasher w may be interposed between the impeller 22 and the impeller bolt28.

The impeller 22 is provided with a confronting surface 26 correspondingto the slanted surface 18 at the front end portion thereof. Therefore,an intersecting point of lines extended from the confronting surface 26is also positioned on the central axis x of the shaft 82. The coolanthaving flowed into the water pump 1 may be smoothly guided andperformance of the water pump 1 may be improved as a consequence ofdisposing centers of the impeller 22 and the rotor 200 that are rotatingelements of the water pump 1 and a center of the stator 101 that is afixed element of the water pump 1 on the central axis x.

In addition, the impeller 22 is divided into a plurality of regions by aplurality of blades 24. The coolant having flowed into the plurality ofregions is pressurized by rotation of the impeller 22.

The body 30 has a hollow cylindrical shape that is opened rearward, andis engaged to the rear end of the pump cover 10. The body 30 includes afront surface 32 forming the volute chamber 16 with the pump cover 10,the stator chamber 42 that is formed at an exterior circumferentialportion of the body 30 and in which the stator 101 is mounted, and therotor chamber 38 that is formed at an interior circumferential portionof the stator chamber 42 and in which the rotor 200 is mounted.

The front surface 32 of the body 30 is provided with the cover mountingportion 44, a first stator mounting surface 40, a first bearing mountingsurface 48, and a penetration hole 34 formed sequentially from anexterior circumference to a center thereof.

The cover mounting portion 44 is engaged to the rear end portion 20 ofthe pump cover 10. Sealing means such as an O-ring O may be interposedbetween the cover mounting portion 44 and the rear end portion 20 inorder to prevent leakage of the coolant from the volute chamber 16.

The first stator mounting surface 40 is protruded rearward from thefront surface 32, and defines a boundary between the stator chamber 42and the rotor chamber 38. In a state that the sealing means such as anO-ring O is mounted at the first stator mounting surface 40, the frontend of the stator 101 is mounted at the first stator mounting surface40.

The first bearing mounting surface 48 is protruded rearward from thefront surface 32. A first bearing 94 is interposed between the firstbearing mounting surface 48 and the front end portion of the shaft 82 inorder to make the shaft 82 smoothly rotate and to prevent the shaft 82from being inclined.

The penetration hole 34 is formed at a middle portion of the frontsurface 32 such that the front end portion of the shaft 82 is protrudedto the volute chamber 16 through the penetration hole 34. The impeller22 is fixed to the shaft 82 in the volute chamber 16. It is exemplarilydescribed in this specification that the impeller 22 is fixed to theshaft 82 by the impeller bolt 28. However, the impeller 22 may bepress-fitted to an exterior circumference of the shaft 82.

Meanwhile, a connecting hole 36 is formed at the front surface 32between the first stator mounting surface 40 and the first bearingmounting surface 48. Therefore, the rotor chamber 38 is fluidlyconnected to the volute chamber 16. Heat generated at the shaft 82, therotor 200, and the stator 101 by operation of the water pump 1 is cooledby the coolant flowing in and out through the connecting hole 36.Therefore, durability of the water pump 1 may improve. In addition,floating materials in the coolant are prevented from being accumulatedin the rotor chamber 38.

The rotor chamber 38 is formed at a middle portion in the body 30. Theshaft 82 and the rotor 200 are mounted in the rotor chamber 38.

A stepped portion 83, the diameter of which is larger than that of theother part, is formed at a middle portion of the shaft 82. According toan exemplary embodiment of the present invention, a hollow shaft 82 maybe used. A spline portion (not shown) may be formed at an exteriorcircumference of the stepped portion 83 along the central axis x.

The rotor 200 is fixed on the stepped portion 83 of the shaft 82, and isformed in an unsymmetrical shape. Thrust is exerted on the shaft 82toward the front surface 32 by the unsymmetrical shape of the rotor 200and a pressure difference between the volute chamber 16 and the rotorchamber 38. The thrust generated at the shaft 82 pushes the shaft 82toward the front surface 32. Thereby, the stepped portion 83 of theshaft 82 may be interfere and collide with the first bearing 94 and thefirst bearing 94 may be damaged, accordingly. In order to preventinterference and collision of the stepped portion 83 of the shaft 82 andthe first bearing 94, a cup 100 is mounted between the stepped portion83 of the shaft 82 and the first bearing 94. Such a cup 100 is made ofan elastic rubber material, and relieves the thrust of the shaft 82exerted to the first bearing 94.

Meanwhile, in a case that the cup 100 directly contacts the firstbearing 94, the thrust of the shaft 82 exerted to the first bearing 94can be relieved. However, rotation friction may be generated between thefirst bearing 94 and the cup 100 of a rubber material, and therebyperformance of the water pump 1 may be deteriorated. Therefore, a thrustring 98 is mounted between the cup 100 and the first bearing 94 in orderto reduce the rotation friction between the first bearing 94 and the cup100. That is, the cup 100 reduces the thrust of the shaft 82 and thethrust ring 98 reduces the rotation friction of the shaft 82. It isexemplarily described in this specification that a groove is formed atan exterior circumference of the cup 100 and the thrust ring 98 ismounted in the groove. However, a method for installing the thrust ring98 to the cup 100 is not limited to the exemplary embodiment of thepresent invention. For example, a groove may be formed at a middleportion of the cup 100 and the thrust ring 98 may be mounted in thisgroove. Further, it is to be understood that any thrust ring 98interposed between the cup 100 and the first bearing 94 may be includedin the spirit of the present invention.

The rotor 200 includes a rotor core 86, a permanent magnet 88, a rotorcover 84, and a rotor case 90.

As shown in FIG. 2 and FIG. 5, the rotor core 86 has a hollowcylindrical shape and is fixed to the stepped portion 83 of the shaft 82by press-fitting or welding, or is splined to the stepped portion 83 ofthe shaft 82. It is exemplarily described in this specification that therotor core 86 is splined to the stepped portion 83 of the shaft 82. Forthis purpose, a coupling groove 204 is formed at an interiorcircumference of the rotor core 86 along the central axis x and issplined to the stepped portion 83.

A plurality of guiding protrusions 202 is formed at the exteriorcircumference of the rotor core 86 along the central axis x, and aplurality of recesses 203 is formed between the guiding protrusions 202along the central axis x. In addition, the permanent magnets 88 areinsertedly mounted in each recess 203. Therefore, the plurality ofguiding protrusions 202 prevents the permanent magnet 88 from rotating.In addition, the plurality of guiding protrusions 202 does not coverboth ends of the permanent magnet 88 so as to limit axial movement ofthe permanent magnet 88. If the guiding protrusion 202 covers both endsof the permanent magnet 88, magnetic flux generated by the permanentmagnet 88 may leak. Such a leakage of the magnetic flux causes that themore and the larger permanent magnet 88 should be used. Therefore, sizeof the water pump 1 may increase. According to an exemplary embodimentof the present invention, the guiding protrusion 202, however, does notcover both ends of the permanent magnet 88, and thus leakage of themagnetic flux may be reduced. Therefore, sufficient capacity of thewater pump 1 may be achieved without increasing the size of the waterpump 1.

The permanent magnet 88 is mounted in the recess 203 formed at theexterior circumference of the rotor core 86. The permanent magnet 88includes N pole and S pole and is mounted in such a manner that the Npole and the S pole are alternately disposed.

As shown in FIG. 2 and FIG. 4, a pair of rotor covers 84 is mounted atboth ends of the rotor core 86 and the permanent magnet 88. A permanentmagnet guider 201 is formed at an interior circumference of the rotorcover 84 such that movement of the permanent magnet 88 mounted at therotor core 86 along the central axis x is restricted. Therefore, therotor cover 84 primarily fixes the rotor core 86 and the permanentmagnet 88, and is made of copper or stainless steel that has highspecific gravity. In addition, the rotor cover 84, as shown in FIG. 7,is formed of a plurality of balance holes 205. If the rotor 200 ismanufactured, it is checked whether the rotor 200 is rotationallybalanced. If the rotor 200 is not rotationally balanced, noise orvibration may occur when the water pump 1 operates. Thereby, performanceof the water pump 1 may be deteriorated. Therefore, positions of thebalance holes 205 are changed such that the rotor 200 is rotationallybalanced.

In a state in which the rotor core 86 and the permanent magnet 88 aremounted to the rotor cover 84, the rotor case 90 wraps exteriorcircumferences of the rotor core 86 and the permanent magnet 88 so as tosecondarily fix them. The rotor case 90 is made of a bulk mold compound(BMC) including a potassium family that has a low coefficient ofcontraction. A method for manufacturing the rotor case 90 will bebriefly described.

The rotor core 86 and the permanent magnet 88 are mounted to the rotorcover 84, and the rotor cover 84 to which the rotor core 86 and thepermanent magnet 88 are mounted is inserted in a mold (not shown). Afterthat, the bulk mold compound including the potassium family is meltedand high temperature (e.g., 150° C.) and high pressure BMC is flowedinto the mold. Then, the BMC is cooled in the mold. As described above,if the rotor case 90 is made of BMC having the low coefficient ofcontraction, the rotor case 90 can be precisely manufactured. Ingeneral, the coefficient of contraction of a resin is 4/1000-5/1000, butthe coefficient of contraction of the BMC is about 5/10,000. If therotor case 90 is manufactured by flowing the high temperature resin intothe mold, the rotor case 90 is contracted and does not have a targetshape. Therefore, if the rotor case 90 is manufactured by the BMCincluding the potassium family that has the low coefficient ofcontraction, contraction of the rotor case 90 by cooling may be reducedand the rotor case 90 may be precisely manufactured. In addition, sinceBMC including the potassium family has good heat-radiating performance,the rotor can be cooled independently. Therefore, the water pump 1 maybe prevented from being heat damaged.

In addition, according to a conventional method for manufacturing therotor, the permanent magnet is fixed to the exterior circumference ofthe rotor core with glue. However, as the rotor rotates, hightemperature and high pressure are generated near the rotor. Thereby, theglue may be melted or the permanent magnet may be disengaged from therotor core. The permanent magnet 88 mounted to the rotor core 86, on thecontrary, is fixed primarily by the rotor cover 84 and secondarily bythe rotor case 90 according to an exemplary embodiment of the presentinvention. Thus, the permanent magnet 88 may not be disengaged from therotor core 86.

The stator chamber 42 is formed in the body 30 at a radially outerportion of the rotor chamber 38. The stator 101 is mounted in the statorchamber 42.

The stator 101 is fixed to the body 30 directly or indirectly, andincludes a stator core 102, an insulator 104, a coil 108, and a statorcase 109.

The stator core 102 is formed by stacking a plurality of pieces made ofa magnetic material. That is, the plurality of thin pieces is stacked upsuch that the stator core 102 has a target thickness.

The insulator 104 connects the pieces making up the stator core 102 toeach other, and is formed by molding a resin. That is, the stator core102 formed by stacking the plurality of pieces is inserted in a mold(not shown), and then molten resin is injected into the mold. Thereby,the stator core 102 at which the insulator 104 is mounted ismanufactured. At this time, coil mounting recesses 106 are formed atfront and rear end portions of the stator core 102 and the insulator104.

The coil 108 is coiled at an exterior circumference of the stator core102 so as to form a magnetic path.

The stator case 109 wraps and seals the stator core 102, the insulator104, and the coil 108. The stator case 109, the same as the rotor case90, is manufactured by insert molding the BMC including the potassiumfamily.

In addition, when the stator case 109 is insert molded, a Hall sensor112 and a Hall sensor board 110 may also be insert molded. That is, thestator 101, the Hall sensor 112, and the Hall sensor board 110 may beintegrally manufactured as one component.

The Hall sensor 112 detects the position of the rotor 200. A mark (notshown) for representing the position thereof is formed at the rotor 200,and the Hall sensor 112 detects the mark in order to detect the positionof the rotor 200.

The Hall sensor board 110 controls a control signal delivered to thestator 101 according to the position of the rotor 200 detected by theHall sensor. That is, the Hall sensor board 110 makes a strong magneticfield be generated at one part of the stator 101 and a weak magneticfield be generated at the other part of the stator 101 according to theposition of the rotor 200. Thereby, initial mobility of the water pump 1may be improved.

A case mounting portion 46 is formed at an exterior surface of the rearend of the body 30.

The driver case 50 is engaged to the rear end of the body 30, and isformed of a case surface 52 at a front end portion thereof. The rotorchamber 38 and the stator chamber 42 are formed in the body 30 byengaging the driver case 50 to the rear end portion of the body 30. Abody mounting portion 60 is formed at an external circumference of thefront end portion of the driver case 50 and is engaged to the casemounting portion 46 by fixing means such as a bolt B.

The case surface 52 is provided with an insert portion 54, a secondstator mounting surface 56, and a second bearing mounting surface 58formed sequentially from an exterior circumference to a center thereof.

The insert portion 54 is formed at an external circumferential portionof the case surface 52 and is protruded forward. The insert portion 54is inserted in and closely contacted to the rear end portion of the body30. Sealing means such as an O-ring O is interposed between the insertportion 54 and the rear end portion of the body 30 so as to close andseal the stator chamber 42.

The second stator mounting surface 56 is protruded forward from the casesurface 52 so as to define the boundary between the stator chamber 42and the rotor chamber 38. The rear end of the stator 101 is mounted atthe second stator mounting surface 56 with a sealing means such as anO-ring O being interposed. The stator chamber 42 is not fluidlyconnected to the rotor chamber 38 by the O-ring O interposed between thefirst stator mounting surface 40 and the front end of the stator 101 andthe O-ring O interposed between the second stator mounting surface 56and the rear end of the stator 101. Therefore, the coolant having flowedin the rotor chamber 38 does not flow to the stator chamber 42.

The second bearing mounting surface 58 is protruded forwardly from thecase surface 52. A second bearing 96 is interposed between the secondbearing mounting surface 58 and the rear end portion of the shaft 82 soas to make the shaft 82 smoothly rotate and to prevent the shaft 82 frombeing inclined.

The rear end of the driver case 50 is open. The driver chamber 64 isformed between the driver case 50 and the driver cover 70 by engagingthe driver cover 70 of a disk shape to the rear end of the driver 50 byfixing means such as a bolt B. For this purpose, a protruding portion 72is protruded forward from an exterior circumference of the driver cover70, and this protruding portion 72 is inserted in and closely contactedto an exterior circumference 62 of the rear end of the driver case 50.Sealing means such as an O-ring O is interposed between the protrudingportion 72 and the exterior circumference 62 so as to prevent foreignsubstances such as dust from entering the driver chamber 64.

The driver 80 controlling operation of the water pump 1 is mounted inthe driver chamber 64. The driver 80 includes microprocessors and aprinted circuit board (PCB). The driver 80 is electrically connected toa controller (not shown) disposed at an exterior of the electric waterpump 1 through a connector 74 and receives a control signal of thecontroller. In addition, the driver 80 is electrically connected to theHall sensor board 110 so as to transmit the control signal received fromthe controller to the Hall sensor board 110.

Meanwhile, the driver chamber 64 is isolated from the rotor chamber 38by the case surface 52. Therefore, the coolant in the rotor chamber 38does not flow into the driver chamber 64.

Hereinafter, the stator 101 of the electric water pump 1 according to anexemplary embodiment of the present invention will be described infurther detail with reference to FIG. 3.

FIG. 3 is a perspective view showing a stator of an electric water pumpaccording to an exemplary embodiment of the present invention.

As shown in FIG. 3, a plurality of fixing grooves 105 are formed at theexternal circumference of the rear end of the stator case 109. Theinsert portion 54 is inserted in the fixing groove 105 so as to limitrotational and axial movements of the stator 101 according to therotation of the rotor 200. Such a fixing groove 105 can be formedtogether with the stator case 109 when the stator case 109 is insertmolded, and an additional process or an additional device is notrequired for forming the fixing groove 105. Therefore, processes formanufacturing the stator 101 do not increase. In addition, since thestator 101 is fixed to the body 30 neither with glue nor bypress-fitting, the stator 101 can be easily disassembled from the body30. Therefore, if the stator 101 is out of order, the stator 101 can beeasily replaced.

In addition, as shown in FIG. 2, the interior circumference of thestator case 109 forms a part of the rotor chamber 38. As describedabove, the coolant flows into the rotor chamber 38 and moves in therotor chamber 38 by rotation of the shaft 82 and the rotor 200. Since astator groove 122 is formed at the interior circumference of the statorcase 109 along the length direction thereof, the coolant in the rotorchamber 38 flows along the stator groove 122 and removes floatingmaterials attached to the interior circumference of the stator case 109.The shape of the stator groove 122 can be easily determined by a personof ordinary skill in the art considering the flow of the coolant in therotor chamber 38.

Further, in order to reduce vibration and noise according to therotation of the rotor 200 and to reduce vibration generated when avehicle drives, a plurality of damping holes 120 are formed at thestator case 109. Vibration and noise according to the rotation of therotor 200 and vibration generated when the vehicle drives are absorbedby movement of gas in the stator chamber 42 through the damping hole120. The position and shape of the damping hole 120 can be easilydetermined by a person of ordinary skill in the art according tovibration frequency and pressure frequency of the stator 101. Inaddition, a frothing resin or sound absorbing material may be filled inthe damping hole 120 so as to further reduce vibration and noise.

Meanwhile, the stator groove 122 and the damping hole 120 may be formedat the rotor 200. That is, grooves (not shown) may be formed at theexterior circumference of the rotor case 90 such that the coolant in therotor chamber 38 flows along the grooves and removes the floatingmaterials attached to the exterior circumference of the rotor case 90.In addition, vibration and noise according to the rotation of the rotor(84, 86, 88, and 90) and vibration when the vehicle drives may beabsorbed by forming holes (not shown) at the rotor case 90.

FIG. 7 is a schematic diagram showing processes for manufacturing arotor used in an electric water pump according to an exemplaryembodiment of the present invention.

If the rotor core 86 provided with the plurality of recesses 203 at theexterior circumference thereof is provided as shown in FIG. 7A, thepermanent magnets 88 are inserted in each recess 203 as shown in FIG.7B. At this time, the permanent magnets 88 are mounted in such themanner that the N pole and the S pole are alternately disposed.

After that, the rotor covers 84 are mounted at both ends of the rotorcore 86 and the permanent magnet 88 as shown in FIG. 7C. Thereby, thepermanent magnets 88 are primarily fixed to the rotor core 86.

After that, the rotor case 90 is molded to the exterior circumference ofthe rotor core 86 and the permanent magnet 88 as shown in FIG. 7D.

When the rotor 200 is manufactured as described above, it is checkedwhether the rotor 200 is rotationally balanced. If the rotor 200 is notrotationally balanced, the positions of the balance holes 205 aredetermined in order to keep the rotational balance of the rotor 200.Then, the balance holes 205 are formed at the rotor cover 84.

Since a stator and a rotor that are electrically operated are wrapped bya resin case having waterproof performance according to an exemplaryembodiment of the present invention, performance and durability of anelectric water pump may improve.

In addition, since a Hall sensor and a Hall sensor board are mounted inthe stator and a control signal is changed according to an initialposition of the rotor, initial mobility of the electric water pump mayimprove.

Further, the shape of the rotor core may be optimized so as to minimizeleakage of magnetic flux of the permanent magnet. Therefore, sufficientcapacity of the water pump may be achieved without increasing the sizeof the water pump.

For convenience in explanation and accurate definition in the appendedclaims, the terms “interior”, “exterior”, “inner”, and “outer” are usedto describe features of the exemplary embodiments with reference to thepositions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. An electric water pump apparatus comprising: astator generating a magnetic field according to a control signal; and arotor enclosed by the stator and rotated by the magnetic field generatedat the stator to pressurize coolant, wherein the rotor includes: a rotorcore having a hollow cylindrical shape to receive a shaft therein, andprovided with a plurality of recesses formed by a plurality of guidingprotrusions formed at an exterior circumference of the rotor core alonga length direction; a plurality of permanent magnets respectivelymounted in the plurality of recesses of the rotor core; a front rotorcover covering and being mounted at a front end of the rotor core andfront ends of the plurality of permanent magnets and a rear rotor covercovering and being mounted at a rear end of the rotor core and rear endsof the plurality of permanent magnets, so as to fix the rotor core andthe plurality of permanent magnets to each other, wherein the front andrear rotor covers are separately formed; and a rotor case enclosing anexterior circumference of the rotor core and the plurality of permanentmagnets so as to fix the rotor core and the plurality of permanentmagnets to each other in a state that the rotor core and the pluralityof permanent magnets are mounted at the front and rear rotor covers;wherein the rotor case is made of a bulk mold compound including apotassium family that has a low coefficient of contraction; and whereinthe front and rear rotor covers are provided with at least one balancehole wherein rotational balance of the rotor is adjusted by changing thelocation and number of the at least one balance hole; wherein the statorincludes: a stator core having a hollow cylindrical shape to receive therotor therein and provided with a stator groove at an innercircumference thereof along a length direction; and a stator casemounted at both distal ends of the stator core, and wherein the statorcase is provided with at least one balance hole, wherein rotationalbalance of the stator is adjusted by changing the location and number ofthe at least one balance hole.
 2. The electric water pump apparatus ofclaim 1, wherein the rotor core includes a coupling groove formed alongan inner circumference of the rotor core and the rotor core is splinedto the shaft through the coupling groove.
 3. The electric water pumpapparatus of claim 1, wherein the plurality of permanent magnets ismounted in such a manner that N poles and S poles are alternatelydisposed with respect to one another.
 4. The electric water pumpapparatus of claim 1, wherein the stator case is made of a bulk moldcompound including a potassium family that has a low coefficient ofcontraction.
 5. The electric water pump apparatus of claim 1, whereinthe stator case is provided with a fixing groove and a driver providingthe control signal is slidably and detachably coupled thereto.
 6. Anelectric water pump apparatus comprising: a stator generating a magneticfield according to a control signal; a rotor enclosed by the stator androtated by the magnetic field generated at the stator; a pump coverhaving an inlet through which coolant flows in and an outlet throughwhich pressurized coolant flows out; a body having: a front surfaceforming a volute chamber between the pump cover and the front surface; astator chamber formed at an outer portion of the body in a radialdirection and the stator being mounted in the stator chamber; and arotor chamber formed at an inner portion of the body in a radialdirection, and the rotor being mounted in the rotor chamber, wherein thestator fluidly insulates the rotor chamber from the stator chamber; ashaft having a central axis, fixed to the rotor so as to rotate togetherwith the rotor about the central axis, and mounted in the rotor chamber;an impeller fixed to a front portion of the shaft so as to rotatetogether with the shaft, pressurizing the coolant having flowed inthrough the inlet, and mounted in the volute chamber; a driver casedetachably mounted at a rear end of the body, formed of a case surfaceat a front surface thereof, having a rear surface opened backward, andformed with a driver chamber therein; and a driver mounted in the driverchamber and applying a control signal to the stator, wherein the rotorcomprises: a rotor core having a hollow cylindrical shape, and providedwith a plurality of recesses formed by a plurality of guidingprotrusions formed at an exterior circumference of the rotor core alonga length direction; a plurality of permanent magnets respectivelymounted in the plurality of recesses of the rotor core; a front rotorcover covering and being mounted at a front end of the rotor core andfront ends of the plurality of permanent magnets and a rear rotor covercovering and being mounted at a rear end of the rotor core and rear endsof the plurality of permanent magnets, so as to fix the rotor core andthe plurality of permanent magnets to each other, wherein the front andrear rotor covers are separately formed; and a rotor case enclosing anexterior circumference of the rotor core and the plurality of permanentmagnets so as to fix the rotor core and the plurality of permanentmagnets each other in a state that the rotor core and the plurality ofpermanent magnets are mounted at the front and rear rotor covers;wherein the rotor case is made of a bulk mold compound including apotassium family that has a low coefficient of contraction; and whereinthe front and rear rotor covers are provided with at least one balancehole, wherein rotational balance of the rotor is adjusted by changingthe location and number of the at least one balance hole.